178 CALCAREOUS MANURES-APPENDIX. 



cascades of streams, is the formation called calcareous tufa or travertine, 

 and vulgarly called " marl" in our mountain region, and which is presented 

 in great quantity, and sometimes in enormous masses. 



As lime-stone water so easily parts with the carbonic acid which enables 

 it to hold lime in solution, it can scarcely be supposed that any of the acid 

 remains after the water collects and remains long in the great reservoirs 

 formed in lakes. But whether the water remains impregnated with car= 

 bonic acid, and of course with lime, or has lost both, the effect is the same, 

 and is exhibited most strongly in the remarkable transparency of lakes 

 so formed. Of such, I have never myself witnessed any but of Lake George, 

 in New York. And after the long lapse of time since my short visit to 

 this lake, I cannot remember to what extent the transparency of its waters 

 was asserted, or what my own personal observation ascertained. I only re- 

 member certainly that the depth of water through which very small objects 

 were distinctly visible was very great, and that no ground was left to doubt 

 what is generally asserted and received as true on that head. 



To return to the lands and waters of Prince George county. The 

 water left by heavy rains, standing in shallow pools on the high level wood- 

 land, and flowing off in temporary rivulets, is seen to be colored by vegeta- 

 ble matter even within a mile of James river, just as it is found on the other 

 lands sloping towards the Blackwater. But in either and every known case 

 of such discoloration being caused, it is on poor and acid land. No such 

 effect takes place on calcareous or even neutral soil, no matter how abun- 

 dantly it is provided with dead leaves or other vegetable matter. There- 

 fore jt is manifest that it is not difference of locality, but difference of soil, 

 which causes the different effects of the surplus rain water becoming 

 tinged, and remaining tinged with vegetable extract, or otherwise remain- 

 ing colorless. And also, after the water has been so tinged, that it depends 

 on the difference of chemical composition in the soils over which it passes, or 

 of the streams into which it is discharged, whether the color remains or is 

 quickly discharged. And, as already stated, this difference of action and effect 

 depends on the absence or presence of lime in the soils or waters to which 

 the colored excess of rain water flows. 



It is only in the surplus quantity of rain water, or that which is more 

 than the soil can absorb, that this coloring matter is seen. But it is not the 

 less certain that all of the much greater quantity of water from more gentle 

 and more frequent rains which soak into the earth, must also be more or 

 less tinged with the coloring matter of the leaves and other dead vegeta- 

 ble matter through which the water passes, and must take up in passing all 

 that is then easily soluble, and not chemically combined with some other 

 body. Thus, every gentle and soaking rain probably carries into the soil 

 the greater part of all the then soluble vegetable matter, and that only 

 which is soluble is all that is then completely ready to act as food for plants. 

 The same rain, and the subsequent chemical action of air and warmth, 

 cause the decomposition of the before insoluble vegetable matter to recom- 

 mence, and in a kw days there is a renewed supply of soluble or extractive 

 matter formed in the vegetable cover of the soil, ready to be dissolved and 

 to be carried into the earth by the next succeeding rain. 



Such is Nature's process of furnishing alimentary manure, or the food of 

 plants, to soils. And the source of supply is unlimited ; for it is principally 

 from the atmosphere and water, and by fixing their elements, (oxygen, ni- 

 trogen, hydrogen and carbon,) that the vegetable growths of soils, and con- 

 sequently all alimentary manures, are formed. 



As enormous then as is the continual waste of vegetable extractive mat- 

 ter and manure that is caused by every heavy rain, and which is always 



